Scores on cognitive tests have been very widely reported to have increased through the decades of the last century, a generational phenomenon termed the "Flynn Effect" since it was most comprehensively documented by James Flynn in the 1980's. There has, however, been very little evidence concerning any continuity of the effect specifically into the present century. We here report data from a population, namely young adult males in Denmark, showing that whereas there were modest increases between 1988 and 1998 in scores on a battery of four cognitive tests--these constituting a diminishing continuation of a trend documented back to the late 1950's--scores on all four tests declined between 1998 and 2003/2004. For two of the tests, levels fell to below those of 1988. Across all tests, the decrease in the 5/6 year period corresponds to approximately 1.5 IQ points, very close to the net gain between 1988 and 1998. The declines between 1998 and 2003/4 appeared amongst both men pursuing higher academic education and those not doing so.